Physical and Chemical Changes and Properties

Texture, odor, taste, and sounds are also physical properties. Physical properties are those characteristics or features you can detect with your senses. The most obvious physical properties are those you can see, like color and shape. Texture, odor, taste, and sounds are also physical properties.

Physical Properties ARE ALSO PHYSICAL PROPERTIES Volume, mass, weight, density, melting point, boiling point, and state of matter , ARE ALSO PHYSICAL PROPERTIES

Physical Changes then it is a physical change. If it melts, evaporates, boils, freezes, breaks, dissolves, or does some other thing that does not change the identity of the substance, then it is a physical change.

Physical Changes If we cut a slice of bread, we would still have bread. We have only altered the appearance of the bread. This is an example of a physical change.

Physical Changes If we dissolve sugar in water, it is a physical change because there is no permanent change to either the water or the sugar. We could recover the sugar simply by boiling the water. The water would evaporate and the sugar would be left in the bottom of the beaker. If we boiled the water in a closed system and were able to capture the steam, we could recover the water as well as the sugar.

Physical Changes If you can separate a substance into individual components by using physical means, such as boiling, you are dealing with a mixture. The individual components in a mixture are not chemically bonded to each other.

Physical Properties How could you separate a mixture of sand and iron filings using their physical properties?

Physical Properties What are some physical properties of sand? You could study their physical properties and decide on a strategy. What are some physical properties of sand? What are some physical properties of iron?

Physical Properties Now we’ve separated our sand and iron filings! Since iron has the property of magnetism, You could pass a magnet over the mixture of sand and iron filings. Only the iron filings would adhere to the magnet, leaving the sand behind. Now we’ve separated our sand and iron filings!

Physical Properties Neither one has magnetism. How could you separate a mixture of sand and sugar? Neither one has magnetism. Both are about the same size and texture.

Physical Properties We know that sugar dissolves in water and sand does not. If we add water to the mixture and stir, the sugar will dissolve and the sand will not. Then we could filter our solution so that the sand gets trapped in the filter and the sugar-water goes through the filter.

Physical Properties Now we’ve separated our mixture of sand and sugar! The sugar-water can be heated so the water evaporates, leaving the sugar behind. Now we’ve separated our mixture of sand and sugar!

Physical Properties Viscosity is the resistance to flow. This means that a viscous liquid will not flow easily. Molasses and shampoo are two examples of viscous liquids. Water is not very viscous – it flows easily. How could we test substances to compare their viscosities?

Physical Properties One way to test viscosity is to see how quickly a marble or pearl will fall through the liquid. Another way is to place a small amount on a slick board, then tilt the board and watch it flow.

Physical Properties Density is another physical property. It is the degree of compactness of a substance. It cannot be seen or measured directly. It must be calculated. You must know the mass and volume of the substance.

Chemical Properties A new substance or substances form. Chemical properties are those which can be described when a substance reacts with another substance. A new substance or substances form. A permanent change occurs, and the old substance generally cannot be recovered.

Chemical Properties The ability to burn is a chemical property The ability to react in acid is a chemical property The ability to react in air is a chemical property

Chemical Properties Physical properties can be observed without changing the material – But… …to observe chemical properties, a chemical change, or reaction, must take place

Chemical Changes Chemical reactions or changes can be recognized by noting one or more of the following observations: Bubbling, or the giving off of a gas. Heat or light is produced. Temperature decreases or increases. A precipitate forms. (a solid that forms when 2 solutions/liquids are mixed) A permanent color change has occurred.

It’s a chemical change Chemical Changes If it decomposes If it changes color permanently If it gets colder If it gives off heat If it rusts If it bubbles If it exhibits one or more of these: If it forms a precipitate It’s a chemical change

Chemical Changes Energy is required for chemical reactions to take place – either it is released or gained.

Physical and Chemical Changes Review For each of the following examples, determine if the action is a Physical change or a Chemical change.

The decomposition of ammonium dichromate. Physical or Chemical? The decomposition of ammonium dichromate. Chemical Change

A piece of paper is torn in half. Physical or Chemical? A piece of paper is torn in half. Physical Change

Starches and sugars being broken down during energy production. Physical or Chemical? Starches and sugars being broken down during energy production. Chemical Change

Sugar dissolving in Kool-Aid. Physical or Chemical? Sugar dissolving in Kool-Aid. Physical Change

Wood burning in a fire place. Physical or Chemical? Wood burning in a fire place. Chemical Change

Physical or Chemical? A nail is rusting. Chemical Change

Water vapor condensing to form rain clouds. Physical or Chemical? Water vapor condensing to form rain clouds. Physical Change

Vinegar is mixed with baking soda and bubbles form. Physical or Chemical? Vinegar is mixed with baking soda and bubbles form. Chemical Change

A newspaper yellows in the sun. Physical or Chemical? A newspaper yellows in the sun. Chemical Change

The compression of sediments. Physical or Chemical? The compression of sediments. Physical Change

Physical or Chemical ? Milk sours. Chemical Change